Abstract: Objective Clinical observation and exploration of the relevance of the invalid red blood cells （RBCs） transfusion and the undetectable low titer and irregular antibodies. Methods One hundred and ninety-six patients with invalid RBCs transfusion were selected from 1 987 clinical cases frim Jun 2014 to April 2015. The ratio of low titer irregular antibodies in pre-transfusion samples was retested using LISS/Coombs cards. Simultaneously,the relationship between the lower titer irregular antibodies and pregnancy,volume of blood transfusion,ages,gender,adverse effect of transfusion,etc. Results The percentage of invalid RBCs transfusion in the 1987 cases of transfusionwas 9.9%,,among them,30 cases of undetectable low titer irregular antibodies were screened out. The ineffective RBCs transfusion and low titer irregular antibodies were closely related with the number of pregnancy （χ²=4.32,P=0.04）,volume of blood transfusions （χ²=6.43,P=0.01）,ages （χ²=6.74,P=0.01）,gender （χ²=9.32,P<0.01）,and adverse reactions of blood transfusion （χ²=4.33,P= 0.04）. Conclusion The low titer irregular antibodies is one of the reasons for invalid red blood transfusion,and closely related with the number of pregnancy,ages,gender,volume and adverse reactions of blood transfusion.

Key words: Invalid red blood cells transfusion, Irregular antibodies, Low titer